1. The Field of the Invention
The present invention relates generally to the field of optoelectronic devices. More particularly, the invention relates to systems and methods for controlling operating requirements of an optoelectronic device at various operating temperatures.
2. The Relevant Technology
FIG. 1 shows a schematic representation of the essential features of a typical conventional fiber optic transceiver. The main circuit 1 contains at a minimum transmit and receive circuit paths and power 19 and ground connections 20. The receiver circuit typically consists of a Receiver Optical Subassembly (ROSA) 2 which contains a mechanical fiber receptacle and coupling optics as well as a photodiode and pre-amplifier (preamp) circuit. The ROSA is in turn connected to a post-amplifier (postamp) integrated circuit 4, the function of which is to generate a fixed output swing digital signal which is connected to outside circuitry via the RX+ and RX− pins 17. The postamp circuit 4 also often provides a digital output signal known as Signal Detect or Loss of Signal indicating the presence or absence of suitably strong optical input. The Signal Detect output is provided at output pin 18.
The transmit circuit will typically consist of a Transmitter Optical Subassembly (TOSA) 3 and a laser driver integrated circuit 5. The TOSA contains a mechanical fiber receptacle and coupling optics as well as a laser diode or LED. The laser driver circuit 5 will typically provide AC drive and DC bias current to the laser. The signal inputs for the AC driver are obtained from the TX+ and TX− pins 12. The laser driver circuitry typically will require individual factory setup of certain parameters such as the bias current (or output power) level and AC modulation drive to the laser. Typically this is accomplished by adjusting variable resistors or placing factory selected resistors 7, 9 (i.e., having factory selected resistance values). Additionally, temperature compensation of the bias current and modulation is often required. This function can be integrated in the laser driver integrated circuit or accomplished through the use of external temperature sensitive elements such as thermistors 6, 8.
In addition to the most basic functions described above, some optoelectronic device platform standards involve additional functionality. Examples of this are the TX disable 13 and TX fault 14 pins described in the Gigabit Interface Converter (GBIC) standard. In the GBIC standard (SFF-8053), the TX disable pin 13 allows the transmitter to be shut off by the host device, while the TX fault pin 14 is an indicator to the host device of some fault condition existing in the laser or associated laser driver circuit.
In addition, the GBIC standard includes a series of timing diagrams describing how these controls function and interact with each other to implement reset operations and other actions. Most of this functionality is aimed at preventing non-eyesafe emission levels when a fault condition exists in the laser circuit. These functions may be integrated into the laser driver circuit 5 itself or in an optional additional integrated circuit 11.
Finally, the GBIC standard for a Module Definition “4” GBIC also requires the EEPROM 10 to store standardized ID information that can be read out via a serial interface (defined as using the serial interface of the ATMEL AT24CO1A family of EEPROM products) consisting of a clock 15 and data line 16.
As an alternative to mechanical fiber receptacles, some conventional optoelectronic devices use fiber optic pigtails which are unconnectorized fibers.
Similar principles apply to fiber optic transmitters or receivers.
In order to maximize the performance and product life of an optoelectronic device, it is advantageous to configure the operating parameters of the optoelectronic device so as to perform temperature compensation and minimize jitter over a range of temperatures at a desired “extinction ratio” and optical power level.
One conventional approach uses a fixed set of temperature compensation parameters for all optoelectronic devices whose components and configurations are otherwise identical. Under high-volume manufacturing conditions, however, this approach is not desirable because the performance and behavior of the components comprising an optoelectronic device vary from component to component. Therefore, the use of universal temperature compensation parameters has different temperature and jitter compensation effects on different modules within a class of similarly configured optoelectronic devices, thereby not achieving the desired efficiency for individual optoelectronic devices.
Another approach uses a temperature controller to maintain a steady operating temperature for the optoelectronic device. This approach, however, is generally not feasible for pluggable optoelectronic devices because temperature controllers are typically too big to fit within such devices. For example, the dimensions for a pluggable optoelectronic device specified by GBIC standards are 1.2″×0.47″×2.6″, and the dimensions for an optoelectronic device specified by SFP (Small Form Factor Pluggable) standards are 0.53″×0.37″×2.24″. As pluggable optoelectronic devices become more and more compact, the use of a temperature controller in these devices is becoming less and less feasible. In addition, temperature controllers can be very expensive, thus increasing or rendering infeasible the cost of manufacturing the optoelectronic device.
Accordingly, what is needed is a control circuit for an optoelectronic device, and method to configure the circuit for each individual device so as to minimize jitter and improve the temperature performance for each individual optoelectronic device.